Socinianism is a denial of the Christian Trinity. It was founded in Poland by Laelius and Faustus Socinus, and subsequently was banned by the Catholic Church.

Socinianism summarises the beliefs of the Socinians, followers of Laelius Socinus (died 1562 in Zürich) and of his nephew Faustus Socinus (died 1604 in Poland). Socinianism is one of the many Antitrinitarian sects that came to exist after the Reformation. The Socinian sect became far more wide spread after Faustus Socinus, Laelius Socinus's newphew, became a valued member. In 1638 Socinians were banished by the Catholics in Poland. Up until this point of time it was widely believed that Socinianism would become a dominant belief in Europe. Socinians held views rooted in reason and rejected orthodox teachings on the Trinity and on the divinity of Jesus, as summarised in the Racovian Catechism. They also believed that God's omniscience was limited to what was a necessary truth in the future (what would definitely happen), and did not apply to what was a contingent truth (what might happen). They believed that, if God knew every possible future, human free will was impossible; and as such rejected the "hard" view of omniscience. The Socinians congregated especially in Transylvania, in Poland (see Polish brethren) and in the Netherlands. They were driven from their seat at Raków in 1643. Socinianism is considered to be an antecedent or early form of Unitarianism. (wikipedia) Now there is something I didn't know...